. Purpose: To investigate the effects of a period of resistive inspiratory muscle training (IMT) upon rowing performance. Methods: Performance was appraised in 14 female competitive rowers at the commencement and after 11 wk of inspiratory muscle training on a rowing ergometer by using a 6-min all-out effort and a 5000-m trial. IMT consisted of 30 inspiratory efforts twice daily. Each effort required the subject to inspire against a resistance equivalent to 50% peak inspiratory mouth pressure (PI max ) by using an inspiratory muscle training device. Seven of the rowers, who formed the placebo group, used the same device but performed 60 breaths once daily with an inspiratory resistance equivalent to 15% PI max . Results: The inspiratory muscle strength of the training group increased by 44 Ϯ 25 cm H 2 O (45.3 Ϯ 29.7%) compared with only 6 Ϯ 11 cm H 2 O (5.3 Ϯ 9.8%) of the placebo group (P Ͻ 0.05 within and between groups). The distance covered in the 6-min all-out effort increased by 3.5 Ϯ 1.2% in the training group compared with 1.6 Ϯ 1.0% in the placebo group (P Ͻ 0.05). The time in the 5000-m trial decreased by 36 Ϯ 9 s (3.1 Ϯ 0.8%) in the training group compared with only 11 Ϯ 8 s (0.9 Ϯ 0.6%) in the placebo group (P Ͻ 0.05). Furthermore, the resistance of the training group to inspiratory muscle fatigue after the 6-min all-out effort was improved from an 11.2 Ϯ 4.3% deficit in PI max to only 3.0 Ϯ 1.6% (P Ͻ 0.05) pre-and post-intervention, respectively. Conclusions: IMT improves rowing performance on the 6-min all-out effort and the 5000-m trial.

During maximal exercise in humans, fatigue is preceded by reductions in systemic and skeletal muscle blood flow, O 2 delivery and uptake. Here, we examined whether the uptake of O 2 and substrates by the human brain is compromised and whether the fall in stroke volume of the heart underlying the decline in systemic O 2 delivery is related to declining venous return. We measured brain and central haemodynamics and oxygenation in healthy males (n = 13 in 2 studies) performing intense cycling exercise (360 ± 10 W; mean ± s.e.m.) to exhaustion starting with either high (H) or normal (control, C) body temperature. Time to exhaustion was shorter in H than in C (5.8 ± 0.2 versus 7.5 ± 0.4 min, P < 0.05), despite heart rate reaching similar maximal values. During the first 90 s of both trials, frontal cortex tissue oxygenation and the arterial-internal jugular venous differences (a-v diff) for O 2 and glucose did not change, whereas middle cerebral artery mean flow velocity (MCA V mean ) and cardiac output increased by ∼22 and ∼115%, respectively. Thereafter, brain extraction of O 2 , glucose and lactate increased by ∼45, ∼55 and ∼95%, respectively, while frontal cortex tissue oxygenation, MCA V mean and cardiac output declined ∼40, ∼15 and ∼10%, respectively. At exhaustion in both trials, systemicV O 2 declined in parallel with a similar fall in stroke volume and central venous pressure; yet the brain uptake of O 2 , glucose and lactate increased. In conclusion, the reduction in stroke volume, which underlies the fall in systemic O 2 delivery and uptake before exhaustion, is partly related to reductions in venous return to the heart. Furthermore, fatigue during maximal exercise, with or without heat stress, in healthy humans is associated with an enhanced rather than impaired brain uptake of O 2 and substrates.